Are you aware the code you have above will only enqueue the stylesheet when it's the parent page, ie. your main plugin page, not any of the rest(subpages)... are you checking the top level page when the enqueue fails? (the bbnuke-option-page page).

You don't necessarily need to register the style unless you're likely to re-use it elsewhere... just the enqueue is sufficient if you're only using it inside the plugin..